Energy Storage Science and Technology ›› 2023, Vol. 12 ›› Issue (5): 1570-1588.doi: 10.19799/j.cnki.2095-4239.2023.0093

• New Energy Storage Technologies • Previous Articles     Next Articles

Research progress on positive electrolytes for neutral aqueous organic redox flow battery

Kangkang QU(), Yahua LIU(), Die HONG, Zhaoxi SHEN, Xiaozhao HAN, Xu ZHANG   

  1. College of Chemistry and Chemical Engineering, Hefei University of Technology, Hefei 230009, Anhui, China
  • Received:2023-02-22 Online:2023-05-05 Published:2023-05-29
  • Contact: Yahua LIU E-mail:qukangkang1999@163.com;liuyahua@hfut.edu.cn

Abstract:

Neutral aqueous organic redox flow batteries (AORFB) are a promising electrochemical energy storage technology owing to their low cost, easy performance regulation, and high operational safety. The technology uses water-soluble electromechanical active materials as electrolytes to store and release energy through their reversible oxidation-reduction process under neutral conditions. Their excellent properties make them highly suitable for large-scale grid connection and intelligent distribution in the renewable energy sector. Drawing on current research on neutral AORFBs, this comprehensive review summarizes the development status, main challenges, and future development direction of positive electrolytes based on ferrocene derivatives and TEMPO derivatives. The modification strategies of ferrocene derivatives and TEMPO derivatives and the development prospects as cathode electrolytes for AORFB are comprehensively summarized and compared. By contrast, TEMPO derivatives have several advantages, such as high redox electrode potential, solubility, battery capacity compared to ferrocene derivatives, and are thus considered to be more promising in practical applications. However, their structural stability is still deemed insufficient for long-term operation. To this end, various modification strategies have been proposed, including the introduction of steric hindrance and electrostatic repulsion, both of which have demonstrated to be and effective. This paper presents a summary and analysis of the degradation mechanism of TEMPO derivatives, which highlights that the breakdown of nitrogen-oxygen bonds owing to proton attack is the primary cause of degradation. The authors suggest the incorporation of importing of protecting groups on the TEMPO main-ring as a potential approach to further improve the long-term structural stability.

Key words: aqueous organic redox flow battery, electrolytes, electrochemistry, ferrocene derivatives, TEMPO derivatives, molecular modification

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